Setting Streamlit widget values via callbacks (dates examples)

widget_callbacks_date_input.py

# Based on discussion here: https://discuss.streamlit.io/t/how-to-work-date-input-with-shortcuts/25377/3
import streamlit as st
from datetime import datetime as dt
import calendar

state = st.session_state

if 'message' not in state:
    state.message = ''

def _change_date_cb(option):
    if option == 'Today':
        state.key_start_date = dt.now()
        state.key_end_date = dt.now()

    elif option == 'Week':
        cal = calendar.monthcalendar(dt.now().year, dt.now().month)
        tdy = dt.now().day
        for i in range(len(cal)):
            if tdy in cal[i]:
                state.key_start_date = dt(dt.now().year, dt.now().month, cal[i][0])
                state.key_end_date = dt(dt.now().year, dt.now().month, cal[i][6])
                break

    elif option == 'Month':
        state.key_start_date = dt(dt.now().year, dt.now().month, 1)
        state.key_end_date = dt(dt.now().year, dt.now().month, calendar.monthrange(dt.now().year, dt.now().month)[1])

    state.message = option

c1, c2 = st.columns(2)
start_date = c1.date_input('Start Date', key='key_start_date')
end_date = c2.date_input('End Date', key='key_end_date')

c1, c2, c3 = st.columns(3)
c1.button('Today', on_click=_change_date_cb, args=('Today',))
c2.button('Week', on_click=_change_date_cb, args=('Week',))
c3.button('Month', on_click=_change_date_cb, args=('Month',))

if state.message:
    st.write('---')
    st.write(f'Dates set for {state.message}')
    st.write(f'`Start: {start_date:%d-%b-%y} | End: {end_date:%d-%b-%y}`')